Origins of plasmaspheric hiss

Geophysical Research Letters, 2013

Both plasmaspheric hiss and chorus waves were observed simultaneously by the two Van Allen Probes in association with substorm-injected energetic electrons. Probe A, located inside the plasmasphere in the postdawn sector, observed intense plasmaspheric hiss, whereas Probe B observed chorus waves outside the plasmasphere just before dawn. Dispersed injections of energetic electrons were observed in the dayside outer plasmasphere associated with significant intensification of plasmaspheric hiss at frequencies down to ~20 Hz, much lower than typical hiss wave frequencies of 100-2000 Hz. In the outer plasmasphere, the upper energy of injected electrons agrees well with the minimum cyclotron resonant energy calculated for the lower cutoff frequency of the observed hiss, and computed convective linear growth rates indicate instability at the observed low frequencies. This suggests that the unusual low-frequency plasmaspheric hiss is likely to be amplified in the outer plasmasphere due to the injected energetic electrons. Citation: Li, W., et al. ( ), An unusual enhancement of low-frequency plasmaspheric hiss in the outer plasmasphere associated with substorm-injected electrons,

Journal of Geophysical Research: Space Physics, 2018

Intense~300-Hz to 1.0-kHz plasmaspheric hiss was studied using Polar plasma wave data. It is found that the waves are coherent in all local time sectors with the wave coherency occurring in approximately three-to five-wave cycle packets. The plasmaspheric hiss in the dawn and local noon time sector are found to be substorm (AE*) and storm (SYM-H*) dependent. The local noon sector is also solar wind pressure dependent. It is suggested that coherent chorus monochromatic subelements enter the plasmasphere (as previously suggested by ray tracing models) to explain these plasmaspheric hiss features. The presence of intense, coherent plasmaspheric hiss in the local dusk and local midnight time sectors is surprising and more difficult to explain. For the dusk sector waves, either local in situ plasmaspheric wave generation or propagation from the dayside plasmasphere is possible. There is little evidence to support substorm generation of the midnight sector plasmaspheric hiss found in this study. One possible explanation is propagation from the local noon sector. The combination of high wave intensity and coherency at all local times strengthens the suggestion that the electron slot is formed during substorm intervals instead of during geomagnetic quiet (by incoherent waves). Plasmaspheric hiss is found to propagate at all angles relative to the ambient magnetic field, θ kB. Circular, elliptical, and linear polarized plasmaspheric hiss have been detected. No obvious, strong relationship between the wave polarization and θ kB was found. This information of hiss properties should be useful in modeling wave-particle interactions within the plasmasphere. Plain Language Summary Plasmaspheric hiss is found to be coherent (at all local times). The coherency occurs in packets of~3 to 5 cycles. For the dawn and noon local time sectors, a scenario of substorm and solar wind pressure generation of outer zone chorus with further propagation into the plasmasphere is supported by the data analysis results. The predominant wave polarization of hiss is found to be elliptical, with some minor presence of circular and linear polarizations. This is in general agreement with theoretical expectations.The presence of intense, coherent plasmaspheric hiss strongly supports the new hypothesis that the electron slot is formed during substorms rather than geomagnetic quiet periods. The loss of relativistic E~1MeV electrons for the inner magnetosphere (L > 6) may be due to wave-particle interactions with coherent plasmaspheric hiss.

Journal of Geophysical Research: Space Physics, 2015

We find that during a large geomagnetic storm in October 2011 the trapped fluxes of >30, >100, and >300 keV outer radiation belt electrons were enhanced at L = 3-4 during the storm main phase. A gradual decay of the trapped fluxes was observed over the following 5-7 days, even though no significant precipitation fluxes could be observed in the Polar Orbiting Environmental Satellite (POES) electron precipitation detectors. We use the Antarctic-Arctic Radiation-belt (Dynamic) Deposition-VLF Atmospheric Research Konsortium receiver network to investigate the characteristics of the electron precipitation throughout the storm period. Weak electron precipitation was observed on the dayside for 5-7 days, consistent with being driven by plasmaspheric hiss. Using a previously published plasmaspheric hiss-induced electron energy e-folding spectrum of E 0 = 365 keV, the observed radio wave perturbation levels at L = 3-4 were found to be caused by >30 keV electron precipitation with flux~100 el cm À2 s À1 sr À1. The low levels of precipitation explain the lack of response of the POES telescopes to the flux, because of the effect of the POES lower sensitivity limit and ability to measure weak diffusion-driven precipitation. The detection of dayside, inner plasmasphere electron precipitation during the recovery phase of the storm is consistent with plasmaspheric hiss wave-particle interactions and shows that the waves can be a significant influence on the evolution of the outer radiation belt trapped flux that resides inside the plasmapause. The influence of plasmaspheric hiss on electron precipitation in the L = 3-4 region has been assessed using pitch angle diffusion codes with wave power distributions based on satellite observations [see Meredith et al., HARDMAN ET AL.

Journal of Geophysical Research, 1975

An instrument to detect the magnetic components of ELF signals propagating in the magnetosphere was carried on Explorer 45. Over 600 hours of observations in the inner magnetosphere near the equatorial plane have been examined. These observations were obtained in late 1971 and the first half of 1972 when the satellite apogee was in the evening and alternoon quadrants. The strongest rfiost persistent signals were plasmaspheric hiss from a few hundred to a few thousand hertz. Broad band signals of 25 m'y were common. Frequently, the hiss terminated abruptly during a satellite pass near and inside the boundary of the plasmasphere. Hiss boundaries were observed usually beyond L = 4 in quiet times, Kp = 0 to 1+, but were frequently beyond apogee near L = 5. During disturbed times, Kp > 4+, hiss boundaries remained near L = 5 from 1600 to 1900 LT but were below L = 4 from 2000 to 2400 LT. The magnetic index best correlated with the hiss boundary near midnight was Dst, the ring current index. The boundary location near midnight ranged from L = 2.5 for Dst =-160 • to L = 5.5 for Dst: 0. The peak intensity of hiss during an orbit occurred most frequently in the alternoon about I RE inside the hiss boundary. The most intense hiss was observed in the recovery phase of magnetic storms at the inner edge of the ring current. The source of the hiss appears to be the outer plasmasphere. Generation of hiss through cyclotron resonance with energetic electrons is the probable source for most of the hiss. Ring current protons, forming a peak in the proton flux between 10 and 100 keV, may be a source for some of the hiss.

Science China-technological Sciences, 2011

The evolution of energetic outer zone electron fluxes during the strong magnetic storm on September 28, 2002 is investigated based on the observations of SAMPEX and GOES-10 satellites. The observations of both satellites showed that energetic electron fluxes increased significantly during the storm recovery phase, and reached the maximum on October 6. The 1.5–14 MeV and 2.5–14 MeV electron fluxes observed by SAMPEX peaked around L=3.5 with values of 6×102 cm−2 s−1sr−1 keV−1 and 5×103 cm−2 s−1 sr−1 keV−1, which were about 10 and 8 times the pre-storm values. At the geostationary orbit, the >0.6 MeV and >2 MeV electron fluxes observed by GOES-10 showed enhancement up to 50 and 30 times. The plasma parameters and whistler-mode chorus waves in the outer radiation belt are also analyzed based on the data from Cluster C3 satellite. Cluster C3 satellite went through the outer radiation belt twice from 1 October to 4 October, and observed whistler-mode chorus waves with high intensity (10−5–10−4 nT2 Hz−1). Numerical calculations indicated that the observed chorus waves were in gyro-resonance with the radiation belt electrons. The current observations and calculations provide new evidence for that the gyro-resonance with chorus waves contribute significantly to the buildup of energetic outer zone electron fluxes during storms.

Journal of Geophysical Research: Space Physics, 2012

On 4 August 2010 a moderate geomagnetic storm occurred with minimum Dst of À65 nT and maximum K p of 7À. Shortly after the onset of this storm, VLF chorus was observed at Marion Island (L = 2.6). Over time the spectral structure of the chorus transformed into a hiss band spanning the same frequency range. The observation of overlapping chorus and hiss suggests that Marion Island was close to the plasmapause at the time of this event, and provides ground-based observational confirmation of the generation mechanism of plasmaspheric hiss from chorus waves outside of the plasmasphere. Chorus observations at Marion Island were not common during this period of the solar cycle and so this event was investigated in detail. The geomagnetic conditions are discussed and geosynchronous particle data and broadband data from two other stations are presented. Empirical models are employed to predict the location of the plasmapause, and its location is inferred from a knee whistler recorded at Dunedin, New Zealand. These show that Marion Island is in the vicinity of the plasmapause during the event. The event is also compared to chorus observed at similar L after the Halloween storms of 2003. The rarity of the chorus observation is quantified using DEMETER VLF data. The DEMETER data, along with the various ground based VLF measurements, allows us to infer temporal and spatial variations in the chorus source region.

Journal of Geophysical Research: Space Physics, 2015

During 18 February to 2 March 2014, the Van Allen Probes encountered multiple geomagnetic storms and simultaneously observed intensified chorus and hiss waves. During this period, there were substantial enhancements in fluxes of energetic (53.8-108.3 keV) and relativistic (2-3.6 MeV) electrons. Chorus waves were excited at locations L = 4-6.2 after the fluxes of energetic were greatly enhanced, with a lower frequency band and wave amplitudes ∼20-100 pT. Strong hiss waves occurred primarily in the main phases or below the location L = 4 in the recovery phases. Relativistic electron fluxes decreased in the main phases due to the adiabatic (e.g., the magnetopause shadowing) or nonadiabatic (hiss-induced scattering) processes. In the recovery phases, relativistic electron fluxes either increased in the presence of enhanced chorus or remained unchanged in the absence of strong chorus or hiss. The observed relativistic electron phase space density peaked around L * = 4.5, characteristic of local acceleration. This multiple-storm period reveals a typical picture that chorus waves are excited by the energetic electrons at first and then produce efficient acceleration of relativistic electrons. This further demonstrates that the interplay between both competing mechanisms of chorus-driven acceleration and hiss-driven scattering often occurs in the outer radiation belts.

Annales Geophysicae, 2004

In the vicinity of the plasmapause, around the geomagnetic equator, the four Cluster satellites often observe banded hiss-like electromagnetic emissions (BHE); below the electron gyrofrequency but above the lower hybrid resonance, from 2 kHz to 10 kHz. We show that below 4 kHz, these waves propagate in the whistler mode. Using the first year of scientific operations of WHISPER, STAFF and WBD wave experiments on Cluster, we have identified the following properties of the BHE waves: (i) their location is strongly correlated with the position of the plasmapause, (ii) no MLT dependence has been found, (iii) their spectral width is generally 1 to 2 kHz, and (iv) the central frequency of their emission band varies from 2 kHz to 10 kHz. All these features suggest that BHE are in fact mid-latitude hiss emissions (MLH). Moreover, the central frequency was found to be correlated with the K p index. This suggests either that these banded emissions are generated in a given f/f ce range, or that there is a K p dependent Doppler shift between the satellites and a possible moving source of the MLH.

Advances in Space Research, 1993

A combination of observations by EISCAT and STARE confirm the existence of bursts of plasma velocity in the auroral electrojet covering about 20 of latitude and 50 of longitude. Where simultaneous measurements of the IMF are available, it can be shown that the auroral electrojet on the nightside is characterised by such bursts even when the XMl' is changing very slowly. cross-correlation between the input of energy from the solar wind and the electric field measured in the electrojet show that with a low-pass filter there is a high and significant correlation, but when the calculation is repeated with a high-pass filter the correlation is low and is not significant at 10%. This suggests that these bursts are not directly driven by changes in the IMP but originate in the magnetotaila conclusion supported by the way in which the bursts appear to drift in the same direction as the average plasma velocity, away from the Harang discontinuity.

Journal of Geophysical Research: Space Physics, 2012

During Corotating Interaction Region (CIR)-driven storms, relativistic electron fluxes in the outer radiation belt decrease in the main phase, followed by a gradual increase in the recovery phase. Recent studies have shown that whistler mode chorus waves play an important role in accelerating the seed electron population to relativistic energies in the outer radiation belt. However, the evolution of chorus waves and their source electrons responsible for the wave excitation during storm various phases is not well understood. In this study we select 72 CIR-driven storm periods over the interval 2007-2011 to perform superposed epoch analysis of the evolution of chorus waves and source electrons in the L* and MLT range extensively observed by THEMIS during various phases of CIR-driven storms. The wave amplitudes and the occurrence of chorus waves substantially increase and peak in the main phase and gradually decrease in the following recovery phase at L* < $7. The phase space density of source electrons at L* < $7 also increases in the main phase followed by a gradual decay in the recovery phase, showing a remarkable consistency with the evolution of chorus waves. Importantly, the evolution of the chorus wave activity and source electron population is highly dependent on the preceding interplanetary magnetic field (IMF) B z orientation. Our results suggest that the increased activity of chorus waves and source electrons may contribute to the enhanced radiation belt electron flux in the recovery phase of CIR-driven storms, but an additional mechanism is probably required to explain the main phase dropout.